1. Field of the Invention
The present invention relates to a process for applying a subbing layer to a plastic film base prior to application of a photographic hydrophilic organic colloid layer (a photographic layer) such as a silver halide photographic emulsion layer, in order to firmly bond the photographic layer to the base.
2. Description of the Prior Art
Heretofore, two techniques have been used to firmly bond a photographic layer to a plastic film base, namely, (i) applying the photographic layer directly after carrying out a surface activation treatment such as chemical processing, an electric discharge treatment or an ultraviolet treatment, etc., and (ii) applying a subbing layer after surface activation and then applying the photographic layer thereto. These processes have been described in, for example, U.S. Pat. Nos. 2,698,241, 2,764,520, 2,864,755, 2,864,756 and 3,475,193 and British Pat. Nos. 788,365, 804,005 and 891,469. Of these processes, the process (ii) has been generally used. Particularly, when the base is polyethylene terephthalate (PET) or polystyrene, the photographic layer does not adhere sufficiently to the base if a subbing layer is not provided after carrying out the surface activation treatment.
The above-described surface activation treatment has the following shortcomings. Namely, when the surface of the base is treated with a solvent, the flatness of the base deteriorates and the residual solvent has a bad influence upon the photographic properties of the photographic layers, particularly, silver halide emulsion layers. Further, in order to obtain sufficient adhesion by the ultraviolet treatment, it is necessary to expose the base to a temperature higher than its glass transition temperature during the treatment and, consequently, its flatness deteriorates remarkably due to a lowering of the modulus of elasticity and contraction by heat, etc. If it is desired to obtain sufficient adhesion by corona discharge, the same result as with the above-described ultraviolet treatment occurs because the treatment similarly requires a high temperature higher than the glass transition temperature.
Moreover, surface activation sometimes not only deteriorates the quality of the support but also detrimentally influences the photographic layers by formation of a very small amount of oligomers or acetaldehyde, etc. Therefore, it has been desired to provide a process for subbing a photographic layer by which sufficient adhesion is obtained without surface activation or with as little surface activation. One technique for improving adhesion involves incorporating a solvent which swells or dissolves the base in the subbing solution. Salicyclic acid, trichloroacetic acid, pyrrole, chloral hydrate, phenol, p-chlorophenol, pyrogallol and resorcinol, etc., have been used as solvents for polyethylene terephthalate. These solvents, however, are generally difficult to handle and poisonous. Further, they endanger the environment and, consequently, their use requires care and is often subject to regulation.
The present inventors have studied a process for applying a subbing layer using an aqueous dispersion of a copolymer comprising (1) a diolefin monomer, (2) one or more vinyl monomers and, if necessary, (3) other components, as described in Japanese Patent Application (OPI) Nos. 112326/76 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application"), Nos. 117617/76, 121323/76, 123139/76 and 139320/76. Further, the inventors have studied blending as described in Japanese patent application (OPI) No. 65422/77 and an addition process as described in British Pat. No. 1,532,517. While these processes improve adhesive strength to some degree without endangering the body or causing environmental problems, they require a considerable heat treatment after application and drying of the subbing layer in order to obtain sufficient adhesive strength and, consequently, they are disadvantageous from the viewpoint of operation and cost.